GCSE · Basic probability

Probability of a single eventExam-style questions

Why a probability is a share of the whole — so it lives between 0 and 1, why P(A) = favourable ÷ total needs equally likely outcomes, and how the "it all adds to 1" rule drives complements, missing table entries and expected numbers.

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13 questions · GCSE (Higher) level · mark scheme and worked solution on each · no sign-up to try

DifficultyAll Level 1 Level 2 Level 3 Level 4 Level 5

1
A bag contains only blue beads, green beads and white beads.

A bead is taken at random from the bag.

The probability that the bead is blue is $\frac{1}{4}$ .

The probability that the bead is green is three times the probability that the bead is white.

(a) Work out the probability that the bead is white.

There are 96 beads in the bag.

(b) Work out the number of green beads in the bag.

Alex takes a bead at random, records its colour and puts it back. He does this 96 times.

Alex says, "The number of times I record a green bead will be exactly the same as the number of green beads in the bag."

(c) Explain why Alex is wrong.
Level 5 · 7 marksTry it